/ˌjuːˈfiːˈaɪ/
noun — "modern firmware interface replacing legacy BIOS."
UEFI, short for Unified Extensible Firmware Interface, is a modern firmware interface for computers that replaces the legacy BIOS. It provides a flexible and extensible environment for bootstrapping operating systems, initializing hardware, and enabling advanced system features. UEFI standardizes the interaction between system firmware and the operating system, supporting large disks, secure boot, and modular firmware components.
Technically, UEFI is stored in non-volatile flash memory on the motherboard and executed by the CPU during the early stages of boot. It supports a richer pre-boot environment, including graphical interfaces, network booting, and runtime services that BIOS lacks. UEFI reads the GUID Partition Table (GPT) to locate bootable partitions, enabling disks larger than 2 TB and more than four primary partitions, addressing MBR limitations.
Core components of UEFI include:
- Boot Manager: Identifies and launches boot loaders or operating systems.
- Device Drivers: Provides low-level control for hardware initialization during pre-boot.
- System Table: Offers runtime services and interfaces for the OS to query firmware capabilities.
- Secure Boot: Ensures that only trusted software is executed during startup, protecting against malware or unauthorized OS loaders.
In workflow terms, UEFI executes as follows: upon power-on, the CPU runs UEFI firmware from flash memory, initializes hardware components, executes POST routines, enumerates devices, reads the GPT to identify bootable partitions, and launches the operating system loader. During runtime, it can provide services such as clock, memory, or firmware update interfaces to the OS.
A simple illustrative pseudo-code for UEFI boot flow:
uefi_init()
check_secure_boot()
enumerate_devices()
boot_partition = find_boot_partition(GPT)
load_bootloader(boot_partition)
transfer_control_to_os()
Conceptually, UEFI is like a modern air traffic control tower: it coordinates and validates all incoming and outgoing operations (hardware initialization and OS boot), ensures security and safety (Secure Boot), and provides rich services to facilitate smooth and reliable system operations beyond the capabilities of the old BIOS.
See BIOS, GUID Partition Table, CPU.